The present invention relates to an apparatus for analyzing the response of optical devices, and more particularly, to an apparatus for analyzing a two port optical device without requiring that the device be reconnected during the measurement process.
There are a large number of optical devices that have two or more ports which receive and transmit light signals. Optical filters, amplifiers, and multiplexers are but a few examples of such devices. These optical components require specific portal characteristics to allow their use in optical networks. Properties such as optical insertion loss, polarization dependence, chromatic dispersion, and reflection coefficients directly affect the performance of optical networks that rely on these devices. Accordingly, equipment and protocols for efficiently testing such devices are required both in research and manufacturing.
To adequately characterize these components, coherent measurement techniques are required. For coherent measurements a stimulus signal is applied to the device and a response signal is extracted therefrom. The response signal must be mixed with a local oscillator signal that has a coherent relationship with the stimulus signal.
To simplify the following discussion, consider the case of a two-port device such as an optical amplifier. To characterize the device a signal is applied to a first port, and the output from the second port together with the signal reflected back from the first port are analyzed. The phase and polarization of the response signal must be measured with respect to that of the input signal to characterize the device. After the first port has been characterized, the roles of the two ports are reversed. Prior art systems do not provide a means for carrying out these coherent measurement functions.
Broadly, it is the object of the present invention to provide an improved apparatus and method for characterizing optical devices that provides coherent measurements.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.
The present invention is an optical interface device for use in testing a device for its response to a stimulus signal. The interface includes a stimulus input port for receiving a light signal, a test signal output port, and a plurality of device test ports. Each device test port couples a light signal from the interface to a port of a device under test, and couples a light signal from the port of the device under test to the interface. The interface includes a reference signal generator for generating a reference signal and a stimulus signal from the light signal input to said interface. A first optical switch routes the stimulus signal to one of the device test ports, the first optical switch having one output port corresponding to each of the device test ports that is capable of coupling the stimulus signal to a device under test. A second optical switch routes a light signal from the device under test to the test signal output port. The second optical switch has a plurality of input ports, each input port being connected to a corresponding one of the device test ports, and a switch output port coupled to the test signal output port. The interface utilizes a plurality of optical routers, one corresponding to each of the device test ports. Each optical router connects an output of the first optical switch to a corresponding one of the device test ports and connects that device test port to a corresponding one of the second optical switch input ports. The output of the optical routers also provides a signal related to the intensity of the light signal leaving the device test port for use in correcting the data for variations in intensity in the stimulus light signal. The interface may include an optical delay circuit for generating an optical delay between the reference signal and the stimulus signal. The reference signal is preferably combined within the interface with the signal leaving the switch output port of the second optical switch prior to that signal being coupled to the test signal output port. The interface may also include a polarization synthesizer for setting the polarization state of the stimulus signal.